The Barca youth product spent a successful season on loan at Goodison Park in 2013/14, making 29 appearances and scoring three goals, before enduring a torrid time at Sevilla last year, where he spent most of the time on the bench.
Yet the English outfit have now re-signed the Spaniard on a three-year deal for a reported £4.3m, much to the delight of coach Roberto Martinez.
"We are getting an even more mature player now than he was a couple of seasons ago and a player who considers Everton as home,” the coach told the club’s official website.
"This is why we are incredibly excited to have him back here on a permanent basis and to encourage him to grow, develop and mature his enormous talent."
The 21-year-old was equally delighted, writing on Twitter: "I'm back! Once a blue, always a blue!"
Deulofeu becomes Everton’s second signing of the new season, after Tom Cleverly joined on a free transfer from Manchester United following ahis successful loan spell at Aston Villa.